This invention is directed to thermoplastic compositions comprising an aromatic polycarbonate, and in particular impact-modified thermoplastic polycarbonate compositions having improved surface quality.
Polycarbonates are useful in the manufacture of articles and components for a wide range of applications, from automotive parts to electronic appliances. Because of their broad use, particularly in electronic applications, it is desirable to provide polycarbonates with good surface appearance.
One defect encountered in injection molded, filled polymeric material is splay. Splay is manifested as streaking or pale marks at areas on the molded article, particularly adjacent to the location of the mold gate. It is believed that splay occurs when the filled polymeric material is injected into a molding cavity and the material encounters high shear stresses caused by the combination of thickness or dimension variation between the runner and the gate, injection pressure, and a temperature drop from a molten state to the mold temperature. The temperature drop increases the melt viscosity of the filled material, especially at the surface, or skin where splay is manifested.
There remains a need to reduce or eliminate the surface defect of splay that is encountered in molding mineral filled polymeric material, and to provide filled materials with improved surface optical properties.